Past tense of alight; to have descended from something, or landed gently as a bird does on a branch.
From Old English 'alihtan' (to descend from, from 'a-' + 'lihtan' to light/descend). The past tense maintains the original meaning of gently or gracefully coming to rest on something.
Alight is basically the poetic version of 'land'—it's almost always used for something delicate like a butterfly or bird. That's why we say 'she alighted upon the subject' when we mean 'she touched on it gently' in conversation.
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